Add driver API reentrancy support to flash driver

[zephyrbot]

Reported by Kuo-Lang Tseng:

Use locking mechanism to guard critical regions in the driver API so that it will allow the driver to be safe from fibers and task.

(Imported from Jira ZEP-414)

[zephyrbot]

by Kuo-Lang Tseng:

https://gerrit.zephyrproject.org/r/#/c/2283/ in review.

[zephyrbot]

by Kuo-Lang Tseng:

https://gerrit.zephyrproject.org/r/#/c/2283/

[zephyrbot]

by ethan gao:

Verified flash erase/write/read concurrently in task/fiber/isr context